Microsoft wont be buying Nokia (now) because:
-They already have their man on the top. Whatever little rumors swirl around, Ballmer's lap dog will go running to his master.
-There is still too much redundancy in the head count in Nokia.
-Headaches with all of the regulatory investigations with EU

When the rumors of a possible buyout from another company become more evident Microsoft can swoop in and take the shambles of the Nokia smartphone division and Elop will (because he is such a nice guy!) sell a bunch of patents to Microsoft.

I do not like the practices of Microsoft (Apple) but I gotta give it to them. They have cornered the market with a very (albeit evil) strategy and are tip toeing in almost every space on the tech industry.

- Nokia has not much of value left that is from interest for Microsoft. Market share? Gone. Software+services? Already transfered. Hardware? Factories closed and hw is done at 3th party in china now. Patents? They are already sold in pieces. Brand? Microsoft has with Windows an own brand and they just established or are establishing Surface.

Nokia as of now is just unactractive. They need to split and sell of all remaining parts separatly.